This invention relates generally to the field of gas flow-meter devices and more specifically to an orifice assembly for a gas-metering device.
The invention is especially applicable to precisely calibrated gas-metering orifices for metering a flow of gas, such as therapeutic oxygen, at a prescribed rate to a patient. The invention also relates to a flow meter which uses such metering orifices to selectively provide a plurality of accurate gas flow rates and to a pressure regulator unit having all of its component parts retained therein.
In the past, orifice punch devices have been used to make orifices of various sizes for flow meters. Generally with these punch devices, the operator punches an orifice in an element and then moves the element from the punch device to a separate flow testing device for measurement of the flow therethrough. If a greater rate of flow is required, the element is transferred back to the punch device for further punching. The transfer of the element back and forth, for further punching and testing is continued until the orifice is properly sized. Such a procedure is an inefficient use of the operator's time. In the alternative, the operator punches a series of elements forming a similar size first orifice in each. This process is then, in turn, repeated, forming a different size second orifice in each of the elements and so forth. While this procedure increased efficiency it also necessitated a great deal of uniformity in the elements prepared, thus the capability of custom designing an element for a specific need or use was severely restricted.
U.S. Pat. No. 4,241,896 to Voege describes forming a calibrated oxygen-metering aperture wherein a plug is progressively pressed into a hole in a valve body. The plug has in its surface a scored slot of progressively decreasing cross-sectional area which defines with the wall of the hole an aperture the size of which depends on the depth to which the plug is inserted in the hole. The gas flow rate through such an orifice is monitored as the plug is pressed into the hole and the plug is stopped at the position which gives the desired calibrated gas flow rate. Thus, the desired flow is attained by plugging the hole.
According to another approach, practiced by applicant and disclosed in patent applications Ser. Nos. 60,943 and 752,295 filed June 19, 1987 and July 5, 1985 respectively, a plurality of orifices are pierced and tapered in a single brass foil disk by a piercing element and the piercing of each orifice is continued until the desired rate of flow through that orifice is attained. This approach can stand improvement because if a mistake is made in piercing one orifice the entire disk may be ruined necessitating calibrating an entire new disk.
U.S. Pat. No. 4,572,477 discloses utilizing an array of relatively thick inserts with orifices therethrough, however, precise calibration of these inserts is exceedingly difficult.